Full Text Article

Introduction

Cobalt is a natural element [1]. The earth’s crust contains 0.0023 % cobalt [2]. It is usually associated with other metals such as copper, nickel, manganese and arsenic [2]. Cobalt is found in the form of cobalamin (vitamin B12), in animal products such as meat, fish, poultry, seafood, milk, cheese and eggs and in inorganic form in plants [3,4]. Vitamin B12 must be provided by ruminants to humans and species with a single gastric pouch because they are unable to produce vitamin B12 from cobalt [5,6]. Cobalt is absorbed by the oral and pulmonary routes. Absorption through intact skin is very low or nil [3]. Oral absorption of cobalt in humans depends on the form of the chemical element, its dose and the nutritional status of the person exposed to it. The absorption of cobalt by the gastrointestinal tract depends on the solubility of the element and the iron deficiency of the exposed person [7]. Cobalt could be cardiotoxic; indeed, cardiomyopathies have been observed in Belgium, the United States and Canada in beer drinkers with cobalt used as a foam-modifying agent [2]. There are other findings on adverse health effects related to cobalt; the repeated absorption of cobalt can also produce hypothyroidism and thyroid hyperplasia. Some cases of polycythemia have also been reported in cobalt-contaminated beer drinkers or exposed workers [3,8]. Cobalt may increase the risk of broncho-pulmonary cancer associated with exposure to hard metals (cobalt associated with tungsten carbide) [3,8]. In vivo and in vitro studies have shown that cobalt salts (dichloride or acetate) are capable of inducing genotoxic alterations such as DNA damage, gene mutations, micronucleus formation, chromosomal aberrations in humans oral (ANSES 2011, Health Canada, 2011). Cobalt deficiency has not been described apart from vitamin B12 deficiencies, of which it is one of the constituents (Basdevant, et al., 2001) [9].

Methodology

Trace element selection

WHO offers a list of the main priority contaminants to be looked for during the TDS (WHO, 2002) [7] but not for nutrients and each country decides on its own priorities? The choice fell on trace element cobalt.

Selection of the core food list

The food list was derived from the food consumption database of a household survey carried out by the National Institute of Statistics (NIS, 2010). This survey was conducted with a sample of 6,500 households representative of the Tunisian population covering the entire geographic (governorate, delegation and district) and socio-economic distribution. There was also a stratification between communal (urban) and non-communal (rural) environments. The house hold samples were rotated (the same house hold was visited two times a day for one week). The observation period of food consumption for each household was of one week. Thus, the researcher analyzed the menu of each main meal (lunch and dinner) twice a day for 7 consecutive days. Each time the researcher would weigh the quantities of food intended to be consumed by the members of the household and which constituted the ingredients for preparing the meals. The researcher also noted the number of people present at that meal. After the meal, the left overs were also evaluated and quantified, including the amounts of food in each dish, in order to only record what had actually been consumed. During each visit, the nature and quantity of all other foods taken between meals were systematically recorded. However, any meals taken outside the household were not taken into account. Only snacks eaten outside were taken into consideration. If a person did not eat a certain meal at home, but did not eat elsewhere either, the portion would be adapted (coefficient that takes into account the “catch-up” during the following meal).Once processed, the consumption data obtained from the National Household Budget and Quality of Life Survey conducted by the National Institute of Statistics of Tunisia (NIS, 2010), enabled us to determine the average amount of food “as consumed”.

The consumption database is in g/week of food “as purchased” per household. The quantities “as purchased” have been converted into “edible parts” of food (by the application of yield coefficients) and then into amount of food “as consumed” (by applying cooking coefficients) (NINFT, 2007).The results of this survey make it possible to approximate the amounts of food “as consumed” rather than “as purchased” in grams per day and per person.

In order to be able to work on data corresponding to the equivalent of “individual consumption”, the total consumption for each household has been converted into data equivalent for one adult. Each individual was assigned a “consumption coefficient” (adult equivalence factor (FAO/WHO/UNU, 2004)).

The amounts weighed are therefore related to the number of persons (individuals who actually consumed them). The results of this survey make it possible to approximate the amounts of food consumed (food “as consumed” rather than “as purchased”) in grams per day and per person and to establish a list of foods to be analyzed representative of the Tunisian diet as described in Table 1.

Foods were classified into food subgroups based on 1) foods of the same category; 2) similar manufacturing methods; 3) a similar composition; and 4) similar cooking methods [10].

This constituted the basis for creating the food item list for the sampling plan. Overall, 42 core food groups were selected covering 97 % of the Tunisian diet.

Sample collection

After listing the most consumed foods, a purchase list and a sampling guide were prepared according to the previous final selection done. This resulted in 42 core food groups representative of the Tunisian diet (quantities, geographic type (regional or national) and seasonality (winter, summer)).Identification of food items to be purchased, their regional distribution and the most consumed brands of food was done according to surveys of the data provided by the various ministries in relation with food control, inter-professional groups (UTICA), inter-professional groups of red meat and milk, poultry and rabbit and distributors.

The investigation about the Tunisian food market production and distribution concerned the entire food chain, from production to final consumption. The data collected enabled us to create a database for each core food category (canned goods, pasta, milk and dairy, poultry and egg products, fish, oil and fats, confectionery, biscuits, water, beverages, sugar and salt) and the identify the geographic zone of the purchase.

The 42 selected core food groups were divided into28 national core food groups including processed and imported food. Samples of these core food groups were purchased at the wholesale market in Tunis (Bir El Kassaa) which centralizes imports from abroad and unprocessed products from many of the country’s governorates. Some samples were purchased from local markets and specific sales outlets for certain foods such as pastries, poultry, etc.

14 regional food groups: these are raw foods produced in different ways and in different environments according to the region (meat, fruits and vegetables) which may have variable levels of contamination. The purchases were made in several places such as the wholesale market in each of the 3 regions chosen for fresh products (if a products was missing, it was purchased at a municipal and/or a weekly market) while other products were acquired at local shops (fresh milk, vegetables, spicy fish, etc.).

Each of the 42core food group samples was, as described in Table 2,a composite sample composed by a weighted proportion of foods according to the respective average amounts of consumption as described in Table 1(e.g. dry legumes are composed of 43.66 % dry beans, 43.7 % chickpeas and 12.65 % lentils) (EFSA,2011) [8].

Analytical method

The cobalt content in the different food groups (fresh fruits and vegetables, cereals, milk and derivatives, meat and derivatives, spices….) and in drinks (including water)was determined by Inductively Coupled Plasma / Atomic Emission Spectrometry (ICP-AES) and inductively Coupled Plasma / Mass Spectrometry (ICP-MS) and this according to the food matrix. The LOD varies from 0.03 to 0.07 mg/Kg and the LOQ varies from 0.1 to 0.2 mg/Kg.

The analytical methods include the following steps: 1st step: Pre-treatment:- Preparation of solid samples for testing (vegetables and fruits, cereal products and derivatives, powdered sugar, spices, meats, fish, eggs, oils and margarines) by homogenization of the sample according to the ‘EN 13804-2002, followed by grinding, homogenization, weighing and placing in a capsule.- Preparation of liquid samples for testing (tap water, milk, carbonated drink) by homogenizing the sample according to EN 13804-2002, followed by weighing and placing in a capsule. 2nd step: Wet mineralization- Hot acid mineralization in the heating block: the sample (solid or liquid) is digested in the presence of concentrated acid (nitric acid), then it is heated at 90 ° C for three hours. For the solid sample, additional heating is done for 4 hours at 160 ° C to obtain a liquid sample. 3rd step: Dosage. The determination of cobalt.

Exposure estimation and treatment of censored data

The processing of censored data (

The cobalt intake was estimated by multiplying the food consumption data for the food group by the cobalt content data for that food group. It is expressed in the usual unit of measurement of the element, that is, in milligrams per kilogram of body weight per day (mg/kg bw/day). The total intake of cobalt is the sum of the cobalt intake in all the aggregated food groups analyzed.

The total intake of cobalt was calculated using the following equation:

- E_ik is the total daily intake of the equivalent adult “i” to pesticide “k” (mg/kg bw/day),

- C_i is the average daily consumption of food “a” by the equivalent adult (one person) “i” (kg/day),

- T_k is the mean content of cobalt “k” in food “a” (mg/kg),- pc_i is the body weight of the equivalent adult “i” (kg).

- n is the total number of foods consumed by the equivalent adult (one person) “i”

In this study, the total daily intake is expressed as the average total daily intake and the 95^th percentile (P95) of daily intake. The average contribution of each food group is expressed as a percentage of the total daily intake.

Results and discussion

Characterization of the danger

WHO considered vitamin B12 rather than cobalt and have only recommended intake for vitamin B12 without setting minimum intakes [11,12]. The risks associated with a high cobalt intake were reviewed by WHO (WHO / FAO, 2004) and the European Food Safety Authority [13] who ultimately decided to take no position and set no maximum value of intake. ANSES, based on the small number of studies available orally, determined a range for a TDI (Tolerable Daily Intake) for the toxic effects of cobalt fixed between 1.6 and 8 μg / kg bw / day without being able to exclude the possibility of toxic effects without threshold [4].

For this study, the nutritional values used as a reference value for the assessment of the adequacy of cobalt intake for the Tunisian adult population are:

- the WHO Minimum Nutritional value Recommended (2.4 μg / d for the 19 to over 65 years of age) because of the absence of Minimum Nutritional requirement value (WHO / FAO, 2004) and

- As the VTR (toxicological reference value ) the lower limit of the TDI (Tolerable Daily Intake) of the interval for toxic effects determined by ANSES which is 1.6 μg / kg bw / day [4].

Exposure assessment

The scenarios used for estimating the cobalt intake of the Tunisian population are the Lower and Upper Bound scenario because the proportion of result -3 (LB) to 0.11 mg / day / eq ad (UB), the mean daily intake on the 5^th percentile varies from 4.42 10^-4 (LB) to 6.84 10^-2 mg / d / eq ad (UB) and the 95th percentile daily intake ranged from 5.37 10^-3 (LB) to 0.161 mg / d / eq ad (UB) (Table 2).

The estimated mean daily intake for cobalt compared to body weight ranged from 2.95 10^-5 (LB) to 1.40 10^-3 mg / kg bw / day (UB), the mean daily intake compared to body weight in the 5^th percentile for the Tunisian population ranged from 5.90 10^-6 (LB) to 9.12 10^-4 mg / kg bw / day (UB) (Table 3).

The main contributors to total mean daily intake in cobalt are tap water (28.55 %), wheat couscous and home-made bread (9 %) and bread (7.03 %).

Risk Characterization

The estimated mean daily intake in cobalt for the Tunisian adult population varies from 92 % at LB to 4378 % at UB of the Minimum nutritional value recommended by WHO. The daily cobalt Intake at the 5th percentile represent 18 % at LB and 2849 % at UB of the Minimum nutritional recommended by WHO.

The mean daily intake in cobalt compared to body weight for the Tunisian adult population represents 1.84 % at LB and 87.57 % at UB percentage of the lower bound of the safety limit (LS) recommended by ANSES. The daily intake of cobalt at the 95th percentile represents 4.47 % at LB and 134.19 % at UB percentage of the lower bound of the LS

The percentage of individuals who have a maximum daily intake in cobalt relative to the body weight more than the lower bound of the LS varies from 0 % at LB to 28.40 % at UB.

Conclusion

In the present study cobalt was quantified in a single core food group (spices) while in the French TDS (ANSES, 2011) and in the Swedish TDS [15], cobalt was quantified in all most foods analyzed. This difference of finding was because of the differences in analytical limits adopted in the search and quantification of cobalt for example in the French TDS (ANSES, 2011) the LOQ adopted was 0.0002 mg / kg which is a hundred times lower than that of the present study.

In the present study, spices represent the only source food identified of cobalt that stands out from other TDSs, which report the highest levels in other food categories such as chocolate and butter such as in the French TDS [4].

The estimated mean daily intake in cobalt for the Tunisian adult population ranged from 2.21 10-3 to 0.11 mg / d / EqAd wich is below that estimated in the US TDS [16] (14 μg / d) in the lower bound scenario but in the upper Bound scenarios the estimated mean daily intake in cobalt for the Tunisian adult population generally covers the Minimum nutritional value recommended by the WHO (92 % to 4378 % of this BNR) [17-22].

Against this, the Intake on the 5th percentile does not cover this BNR in the LB (18.43 %), thus not allowing us to eliminate the possibility of inadequate intake for at-risk populations or populations with inadequate diets.

The mean daily intake estimated in cobalt compared to body weight for the Tunisian adult population is significantly lower than that of the French TDS (ANSES, 2011) in the minimalist scenario (LB).

The overestimation of the maximalist scenario (UB) increases the estimated intake in cobalt. Therefore, the maximalist scenario increases the theoretical estimated intake in cobalt compared to the body weight for the Tunisian adult population, bringing the maximum daily intake almost to 88 % of the adopted LS and beyond this LS (134 %) in the 95th percentile. In view of the particularly high LOQ adopted of the present study which significantly increases the intake the risk of excess cobalt could be ruled out with certainty.

These conclusions, however, should be confirmed by another study with analytical limits lower that detect the presence of cobalt in food more precisely and permit a more realistic assessment of cobalt intake.